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Date: Tue, 21 Oct 2025 16:10:06 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Kohei Enju <enjuk@amazon.com>
Cc: <aleksander.lobakin@intel.com>, <andrew+netdev@lunn.ch>,
 <anthony.l.nguyen@intel.com>, <corbet@lwn.net>, <davem@davemloft.net>,
 <edumazet@google.com>, <horms@kernel.org>, <jacob.e.keller@intel.com>,
 <jiri@resnulli.us>, <linux-doc@vger.kernel.org>,
 <linux-kernel@vger.kernel.org>, <netdev@vger.kernel.org>,
 <pabeni@redhat.com>, <przemyslaw.kitszel@intel.com>, <sx.rinitha@intel.com>
Subject: Re: [PATCH net-next v2 13/14] ixgbe: preserve RSS indirection table
 across admin down/up
Message-ID: <20251021161006.47e42133@kernel.org>
In-Reply-To: <20251021040000.15434-1-enjuk@amazon.com>
References: <20251020183246.481e08f1@kernel.org>
	<20251021040000.15434-1-enjuk@amazon.com>
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On Tue, 21 Oct 2025 12:59:34 +0900 Kohei Enju wrote:
> For example, consider a scenario where the queue count is 8 with user
> configuration containing values from 0 to 7. When queue count changes
> from 8 to 4 and we skip the reinitialization in this scenario, entries
> pointing to queues 4-7 become invalid. The same issue applies when the
> RETA table size changes.

Core should reject this. See ethtool_check_max_channel()

> Furthermore, IIUC, adding netif_is_rxfh_configured() to the current
> condition wouldn't provide additional benefit. When parameters remain
> unchanged, regardless of netif_is_rxfh_configured(), we already preserve
> the RETA entries which might be user-configured or default values, 

User may decide to "isolate" (take out of RSS) a lower queue,
to configure it for AF_XDP or other form of zero-copy. Install
explicit rules to direct traffic to that queue. If you reset
the RSS table random traffic will get stranded in the ZC queue
(== dropped).